package com.purdue.edu.psychotron.shared;

/****************************************************************************
 *  Compilation:  javac UF.java
 *  Execution:    java UF < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/15uf/tinyUF.txt
 *                http://algs4.cs.princeton.edu/15uf/mediumUF.txt
 *                http://algs4.cs.princeton.edu/15uf/largeUF.txt
 *
 *  Weighted quick-union (without path compression).
 *
 *  % java UF < tinyUF.txt
 *  4 3
 *  3 8
 *  6 5
 *  9 4
 *  2 1
 *  5 0
 *  7 2
 *  6 1
 *  # components: 2
 *
 ****************************************************************************/


/**
 *  The <tt>UF</tt> class represents a union-find data data structure.
 *  It supports the <em>union</em> and <em>find</em>
 *  operations, along with a method for determining the number of
 *  disjoint sets.
 *  <p>
 *  This implementation uses weighted quick union.
 *  Creating a data structure with N objects takes linear time.
 *  Afterwards, all operations are logarithmic worst-case time.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/15uf">Section 1.5</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */

public class UF {
	private int[] id;    // id[i] = parent of i
	private int[] sz;    // sz[i] = number of objects in subtree rooted at i
	private int count;   // number of components

	/**
	 * Create an empty union find data structure with N isolated sets.
	 */
	public UF(int N) {
		count = N;
		id = new int[N];
		sz = new int[N];
		for (int i = 0; i < N; i++) {
			id[i] = i;
			sz[i] = 1;
		}
	}

	/**
	 * Return the id of component corresponding to object p.
	 */
	public int find(int p) {
		while (p != id[p])
			p = id[p];
		return p;
	}

	/**
	 * Return the number of disjoint sets.
	 */
	public int count() {
		return count;
	}


	/**
	 * Are objects p and q in the same set?
	 */
	public boolean connected(int p, int q) {
		return find(p) == find(q);
	}


	/**
	 * Replace sets containing p and q with their union.
	 */
	public void union(int p, int q) {
		int i = find(p);
		int j = find(q);
		if (i == j) return;

		// make smaller root point to larger one
		if   (sz[i] < sz[j]) { id[i] = j; sz[j] += sz[i]; }
		else                 { id[j] = i; sz[i] += sz[j]; }
		count--;
	}

}